The present invention relates to balancing systems and more specifically to rotor balancing.
High-speed rotor systems such as those used in flywheel energy systems usually operate in a vacuum environment at a rotation speeds of about 1,000 meters per second. The coefficient of friction of such a passive bearing system is typically extremely low, with a value of about 3.times.10.sup.-7. Accordingly, the rotational efficiency of the rotor is especially sensitive to small amounts of imbalance. Therefore, a precisely balanced rotor is critical to efficient operation.
Static balancing and dynamic balancing are two general approaches that can be used to balance a rotary member. Static balancing is generally used to identify imbalance moments along one axis of the rotor element. Static balancing is generally performed by putting the geometric center of the element on either a gimbal mount or a rotational mount. Both the gimbal mount and the rotational mount typically comprise a mechanical bearing as known by those skilled in the art. Gravity will typically cause the element to move in one or more directions. The direction that the component moves indicates the imbalance moment. This imbalance moment can be compensated by making a small change in mass opposite to the imbalance location to introduce an equal and opposing moment.
When a gimbal mount is used, the geometric center of the element being balanced is placed on the mount which typically comprises a fulcrum or similar device. An imbalance moment on the element provides a torque that tips the imbalanced portion of the element downward. A gimbal mount thus allows the element to move in two dimensions. When a rotational mount is used, the element is tilted at an angle with respect to the direction of gravity such that an imbalance moment causes the imbalanced portion of the element to rotate to the lowest point of the tilt. Thus, a rotational mount allows the element to move in one dimension.
In both static and dynamic balancing, the ability to detect imbalance is limited by the amount of friction in the bearing. The friction in the bearing can create torques that may offset any imbalance moment that is smaller than the friction torque. Such friction may prevent the detection of small degrees of imbalance. Accordingly, as the friction in a bearing increases, the sensitivity of the balancing system decreases. Therefore, it is desirable to limit the amount of friction present in balancing system bearings.